IESL Part II Civil key terms

The maximum pressure a soil or rock mass can support beneath a foundation before shear failure occurs, usually expressed as a pressure or stress and determined from soil strength parameters, footing geometry, and depth of embedment.

A footing that transfers structural loads to soil at a depth less than its width, such as a strip, spread, or pad footing. Design checks include bearing capacity, settlement, and sliding.

A deep foundation element driven or bored into the ground to carry loads through weak strata to stronger soil or rock. Capacity comes from shaft friction, end bearing, or both.

The resistance developed along the shaft of a pile or drilled pier as the surrounding soil opposes relative movement between pile and ground during loading, contributing to the total axial capacity.

The component of deep foundation capacity carried by direct pressure at the pile tip or base against the soil or rock beneath it, distinct from resistance along the shaft.

Downward vertical movement of a structure or ground surface caused by compression of underlying soil, often divided into immediate, primary consolidation, and secondary components. Differential settlement between adjacent supports is usually the more damaging condition.

Time-dependent volume decrease of a saturated soil under sustained load, as water is squeezed out of voids and pore pressure dissipates. In clays this process can take years and governs long-term settlement.

The intergranular stress carried by a soil skeleton, equal to total stress minus pore water pressure. It controls soil strength and compressibility, so changes in groundwater level directly alter effective stress.

The pressure of water filling the voids of a soil or rock mass. Above-hydrostatic values reduce effective stress and can trigger instability, while dissipation of excess pressure drives consolidation settlement.

Loss of soil shear strength when saturated loose sands or silts are shaken and pore pressures rise until effective stress approaches zero, so the ground behaves like a fluid and foundations may sink or tilt.

An in-situ test in which a split-spoon sampler is driven into the ground by a falling hammer, with the blow count (N-value) used to estimate soil density, strength, and liquefaction susceptibility.

An in-situ test pushing an instrumented cone into the ground while recording tip resistance and sleeve friction. Results are used to classify soils and estimate strength and stiffness parameters.

The capacity of a soil or rock to transmit water through its interconnected voids, quantified by the coefficient of permeability. It governs seepage rates, drainage design, and the rate of consolidation.

Movement of water through soil or rock under a hydraulic gradient. Seepage forces reduce stability, and uncontrolled flow can cause piping or internal erosion beneath and around structures.

Internal erosion in which seepage progressively washes fine particles from soil, forming a continuous channel that can lead to sudden failure of embankments, dams, or retaining structures.

The ratio of resisting capacity to applied load or demand, used to ensure that uncertainties in loads, material properties, and analysis do not lead to failure. Values are set by codes for each design case.

The maximum foundation pressure permitted by design, chosen so that bearing capacity is not exceeded and settlement remains within acceptable limits for the structure.

Assessment of whether a natural or engineered slope will resist sliding or rotational failure. It compares driving forces from gravity and seepage with available soil shear strength, often using limit equilibrium methods.

A structure built to hold back soil or other material where a change in ground level is required. Design must check overturning, sliding, bearing pressure, and overall stability.

The horizontal stress exerted by soil on a retaining structure. It is commonly classified as at-rest, active, or passive depending on whether the wall allows the soil to move.

A design philosophy that checks a structure against defined conditions of failure or unserviceability. Ultimate limit states address safety against collapse, while serviceability limit states address deflection, cracking, and settlement.

Composite material in which steel reinforcement carries tensile forces while concrete resists compression. The two materials act together because of bond and similar thermal movement, enabling beams, slabs, and columns.

Concrete in which internal compressive stresses are induced before loading, usually by tensioned steel tendons, to control cracking and permit longer spans or thinner sections. It may be pre-tensioned or post-tensioned.

The thickness of concrete between the outer surface of embedded steel and the nearest exposed concrete face. It protects steel from corrosion and fire, and ensures bond and anchorage.

The ability of a material or structural member to undergo large inelastic deformation without losing strength before failure. Ductile behaviour provides warning of distress and allows redistribution of forces.

The ability of a structure or material to maintain acceptable performance over its design life when exposed to its environment, including resistance to corrosion, abrasion, chemical attack, and freeze-thaw cycles.

The permanent, essentially constant weight of a structure and its fixed attachments, including self-weight of members, finishes, and fixed services. It is estimated from material densities and geometry.

A transient or movable load imposed on a structure by its intended use, such as occupants, furniture, vehicles, or stored goods. Design values are specified in loading codes.

A defined arrangement of simultaneous load effects, with partial or global factors, used to check a structure for a particular limit state. It accounts for the low probability of all loads peaking together.

The internal force acting parallel to a cross-section of a member, tending to slide one part relative to another. Shear force diagrams show how this internal demand varies along the span.

The internal moment at a section of a member caused by external loads acting at a distance, producing tension on one face and compression on the other. Its distribution along the member is plotted as a bending moment diagram.

Twisting of a member about its longitudinal axis produced by eccentric loads or moments. Torsional stresses are highest at the outer surface and require closed sections or dedicated reinforcement to resist.

The displacement of a structural member from its unloaded position under load. Serviceability checks limit deflection to avoid cracking of finishes, ponding, vibration, and visual distress.

A measure of the stiffness of a material in the elastic range, defined as the ratio of tensile or compressive stress to the corresponding strain. It links stress and deformation in structural analysis.

The cross-sectional area of a flowing channel divided by its wetted perimeter. It is used in Manning's and Chezy equations to estimate flow velocity and capacity in open channels and pipes.

An empirical formula relating flow velocity in an open channel to hydraulic radius, channel slope, and a roughness coefficient. It is widely used to size drains, culverts, and natural channels.

Flow of water with a free surface exposed to atmospheric pressure, driven by gravity along a channel slope. Its depth and velocity depend on discharge, channel geometry, and roughness.

A covered conduit, usually under a road or embankment, that conveys water from one side to the other. Design considers hydraulic capacity, inlet and outlet conditions, and scour protection.

Erosion of streambed or bank material around a structure by flowing water, which can undermine bridge piers and abutments. It is assessed using hydraulic and sediment conditions at the site.